Method of treating surfaces



United States '1 atent 3,406,105 METHOD OF TREATING SURFACES Calvin 0. Letendre, Northford, Conn, assignor to Chromium Corporation of America, Waterbury, Conrn, a corporation of Delaware No Drawing. Filed Sept. 3, 1963, Ser. No. 306,359 8 Claims. (Cl. 204-16) This invention relates to a method of treating surfaces. More specifically it relates to a process for filling in pitted areas of basis metal to render the basis metal suitable for subsequent treatment by electroplating.

As is well known to those skilled in the art, there are numerous operations which require that the surface of a basis metal be smooth, i.e., must have a reading as measured by a stylus-type instrument of less than about 125 microinches root mean square, and typically a reading of 8-32 RMS microinches. Such a smooth surface may also be preferably characterized by the absence of any discontinuities, including pits, flaws, or irregularities, which may be greater than about three times the RMS microinch measurement of the surface.

Typical of the surfaces which must be smooth, i.e., free of imperfections of the type noted, may be rolls, drums, castings, or cylinders which may be used in the manufacture of paper, felt, plastics, food, pharmaceuticals, photographic materials, adhesive compositions, etc. Since the process of this invention may readily be used to treat rolls, reference may for purpose of convenience, be hereinafter made to rolls. These surfaces may not function satisfactorily unless they are smooth. Furthermore, it is particularly necessary that this be the case if the surface of the roll is to be electroplated during manufacture or during rebuilding. As is well known, plating with many metals, e.g., chromium, nickel, cadmium, tin, copper, etc., is particularly characterized by the fact that the deposited plate follows the depressions, i.e., pits, indentations, discontinuities, or other irregularities of the basis metal. Accordingly, it is common to carry out a leveling operation prior to electroplating.

Where the surface of the basis metal, e.g., on a roll, is to be rebuilt it may be possible to eliminate the irregularities in the surface by selectively and individually filling each imperfection by (a) welding, or (b) spot plating, or (c) drilling out the holes followed by dowel plugging. This operation must be followed by leveling and polishing before electroplating can be effected. These procedures are very expensive in that they require a considerable expenditure of skilled labor. Furthermore, as is apparent, it may not be possible to utilize these techniques when the surface is very badly pitted and has a myriad of imperfections. In this case, the surface must be reground until a sound level is reached; the metal removed must then be rebuilt.

It is an object of this invention to provide a process for preparing a basis metal to provide a smooth base for subsequent operations. It is a further object to provide a process for preparing a basis metal preparatory to depositing thereon a layer of metal. Other objects will be apparent to those skilled in the art on inspection of the following description.

In accordance with certain of its aspects, the novel process of this invention for electrodepositing a smooth level coating of metal on a basis metal containing surface depressions may comprise filling in the surface depressions with a viscous electrically conductive plastic containing 10%90% flaky iron particles and 90%10% fibrous iron particles; hardening said plastic; removing excess plastic from said basis metal thereby forming a level surface; and electrodepositing a smooth level metal coating on said surface.

The basis metal which may be treated in practice of this invention may typically be a chromium plated steel cylinder which has, over an extended period of use, become worn. Typically the surface of the cylinder or roll may be no longer smooth, i.e., it may contain numerous discontinuities and irregularities which may be greater than about three times the RMS microinch measurement of the surface. These discontinuities may be greater than about 24-96 RMS microinches, and typically 375 RMS microinches.

In practice of this invention, the surface depressions may be filled in with a viscous, electrically conductive plastic. This viscous electrically conductive plastic may contain a resin vehicle and a conductive powder. The conductive powder may be a metal, or a metal oxide such as magnetite Pe o, or cuprous oxide Cu O. Preferably, it will be a metal of Group VIII of the Periodic Table which group includes iron, cobalt, and nickel. Preferably the metal will be iron including iron alloys and steel. Typical metals may include pure iron, wrought iron, cast iron, etc. Hydrogen reduced mill scale from steel may be employed.

It is a feature of the composition of this invention that the preferred conductive powder may be iron and more particularly may include 10%90%, say 50% flaky iron particles and 10%90%, say 50% fibrous iron particles. If the proportion of fibrous iron be increased, the speed of plating may be increased. The flaky iron may be characterized by its blocky, chunky, non-elongated structure wherein all the dimensions of the individual pieces or crystals are of the same order of magnitude, e.g., typically the greatest dimension may not be greater than about twice the larger of the other two dimensions. The flaky iron particles may typically have sharp edges, although they may be rounded. The fibrous iron may be characterized by its dendritic, pine-tree-shaped, attenuated, 0r elongated structure wherein one dimension may be of the order of ten times the greater of the other two.

The flaky, chunky, or blocky iron may be present in the form of coarse particles a substantial portion, typically of which preferably have a particle size of 17774 microns, but preferably 177-149 microns. This may correspond to a range wherein 100% of the particles pass through an SO-mesh U.S. standard screen and 100% of the particles are retained on a IOU-mesh standard screen. Flaky iron particles are available in the form of reduced mill scale.

The fibrous, dendritic, or elongated iron may be present in the form of fine particles a substantial portion, typically 100%, of which preferably have a particle size of about 26-62, and preferably about 44 microns (i.e., its greatest dimension will preferably be about 44 microns). This preferred size may correspond to a range wherein 100% of the particles may pass through a 325-mesh U.S. standard screen. Such a particle may for example be prepared by chopping steel wool by means of, e.g., a threshing type chopper.

Thus the preferred conductive powder may be iron metal containing particles 10%90% of which may be flaky iron particles having a particle size of 149-177 microns and 10%90% of which may be fibrous iron particles having a particle size of about 26-62 microns.

Formation of the compositions useful in practice of this invention may be effected by mixing together one part by weight of resin vehicle with 26, say 3 parts by 3 weight of conductive powder. This may correspond to one part by volume of resin vehicle to 0.66-2, say one part by volume of conductive powder.

Typical resin vehicles which may be used may include polyesters. The preferred resin vehicle may be an unsaturated polyester which may be set or hardened by cross-linking with an ethylenically unsaturated monomer, such as styrene. Typical saturated polyester resins which may be employed may be those formed by the reaction e.g. of phthalic anhydride, isophthalic acid, hexahydrophthalic anhydride, tetrachlorophthalic anhydride, etc. with e.g. ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, dipropylene glycol, etc. Typical unsaturated polyester resins which may be employed may be those wherein the acid (including anhydride) employed may be maleic acid, fumaric acid, citraconic acid, etc.

Illustrative polyester resins which may be employed may include those formed by reaction of the following acid and alcohols:

Acid: Alcohol Phthalic anhydride Ethylene glycol. Isophthalic anhydride Do.

Fumaric acid Glycerine.

Citraconic acid Do.

Phthalic anhydride Propylene glycol.

Do Butylene glycol. Do Diethylene glycol.

Obviously the proportions of resin and conductive powder may vary as hereinbefore set forth. The preferred resins may be those which are liquid at temperature up to about 40 C. and preferably at 25 C.40 C.

Where the polyester resin is formulated from acids and .alcohols which are saturated, the resin may be cured as by heating or by use of oxidizing agent e.g. methyl ethyl ketone peroxide. Where the resin is formulated from a component which is unsaturated, e.g. fumaric acid, it may preferably be thermoset by crosslinking with a vinyl monomer. Typical vinyl monomers may include styrene, diallyl phthalate, vinyl toluene, triallyl cyanurate, methyl vinyl ketone, acrylonitrile, and acrylic esters such .as methyl methacrylate.

In practice of a preferred embodiment of this invention, the conductive plastic may be effected by mixing together the noted amounts of conductive powder e.g. metal with the resin vehicle. Preferably the metal may be blended into the reaction mixture used to prepare the resin, i.e. the mixture containing the components (e.g. acid, alcohol, catalyst, promoter, etc.) of the resin vehicle.

A preferred viscous electrically conductive plastic may thus be formed by combining (a) three parts by weight of a conductive powder and (b) one part by weight of a resin vehicle formed by combining 1-2, say 1.5 moles (i.e. 100200, say 150 parts by weight) of styrene and one mole of polyester formed from equivalent proportion of glycerine (e.g. 184 parts by weight) and fumaric acid (e.g. 348 parts by weight) in the presence of catalyst (e.g. 3-14 parts of 60% methyl ethyl ketone peroxide solution in dimethyl phthalate) and optionally promoter (e.g. 6-7 parts by weight of cobalt naphthenate). (One mole of polyester may be defined as the amount of polyester formed by reacting molar equivalents of the components thereof e.g. two moles of glycerine and three moles of fumaric acid.) This mixture may set within a predetermined time by control of the type and amount of catalyst and promoter. Typically polymerization may be controlled so that the mixture sets in 10-60 minutes, say minutes.

Other illustrative compositions which may be employed in practice of this invention may be made by forming a polyester resin by reacting two equivalents of glycerine with three equivalents of fumaric acid, further reacting this with 1.5 equivalents of styrene, and adding methyl ethyl ketone peroxide catalyst. This resin vehicle mixture may be blended with three times its weight of iron powder, the following illustrative compositions being preferred:

TABLE I Flaky iron Fibrous iron Percent Particle size (app) Percent Particle size (app) microns microns The preferred viscous electrically conductive plastic may be one which immediately prior to polymerization may have a viscosity at application temperature which is sufiicient to permit ready application on to the basis metal surface and to readily fill the pits, indentations, etc. thereon.

Treatment of the basis metal containing surface depressions prior to application of the electrically conductive plastic may include a cleaning operation. Prefer-ably this may be done by contact with an organic cleaner including benzene, or preferably trichloroethylene. The surface may then preferably be blasted with silicon carbide or aluminum oxide grit, typically No. 240, and then cleaned again, typically with trichloroethylene. This action may remove disoriented or disturbed metal, peen the microscopic pits, and increase the surface area.

Preferably the basis metal may be heated to at least about 65 C. and preferably to about C. during which time any gases present in the metal, including those entrapped during chromium plating, may be liberated. Preferably heating may be continued for 3-6 hours, typically 4 hours during which time the roll may become completely degassed.

At the end of the degassing period, the basis metal may be permitted to cool, typically to room temperature. When the temperature of the roll is 35 C.-65 C., the conductive plastic may be applied to the basis metal. As the polymerizing-hardening mixture is disposed over the entire surface of the basis metal, it may be wiped or scraped into the holes, pits, or other indentations therein. Preferably it may be permitted to remain in position for 12-24 hours, say 24 hours as the roll cools to and remains at room temperature, during which time, the conductive plastic may polymerize or harden.

After hardening, the excess of conductive plastic may be removed as by grinding, sanding, or belting with abrasive belts to leave a substantially smooth surface where the depressions, pits, etc. of which may have been filled with the conductive plastic. It is a particular characteristic of this noval composition, because it contains the noted combination of flaky and fibrous iron particles, that it is electrically conductive i.e. readily platable. It is sufficiently conductive to permit rapid electroplating thereon.

The so-prepared basis metal may be plated with desired metal, typically chromium to yield a product chromiumplated roll possessing a surface which is completely level and smooth. Chromium plating may be effected by maintaining the piece as cathode for e.g. 5 hours in a bath containing 250 g./l. chomic acid and 2.5 g./1. sulfate ion derived from sulphuric acid, at temperature of 34 C.- 72 C. and a cathode current density of 8-90, preferably 12-45 amperes per square decimeter.

In accordance with a specific embodiment, a chromium plated steel roll which had been used for an extended period of time and which contained numerous pits, indentations, discontinuities and irregularities, 'may be treated by the process of this invention. The roll may be vapor degreased by trichloroethylene, cleaned by blasting with No. 240 grit aluminum oxide, and vapor degreased with trichloroethylene. The roll may then be heated to about 95 C. for 4 hours during which time any gases occluded therein may be liberated.

The heated roll may be permitted to cool and, after it has reached 65 C., the conductive plastic may be applied thereto. In this specific embodiment, the plastic may be formed by mixing equivalent portions of glycerine (2 moles or 184 parts by weight) and fumaric acid (3 moles or 348 parts by weight) with 1.5 moles or 156- parts by weight of styrene, 8 parts of polymerization catalyst (a 60% solution of methyl ethyl ketone peroxide in dimethyl phthalate); with the same amount by volume of a mixture of 50% flaky particles having a particle size of 74-177, preferably 149-177 microns and 50% fibrous iron particles having a particle size of about 2662 microns.

This conductive plastic may be wiped over the surface of the roll by use of metal knives or blades. The roll may then be permitted to stand for 24 hours during which time it cools to room temperature. At the end of this period, the conductive plastic may harden. The excess of hardened plastic may be removed by grinding or belting thereby leaving a readily platable, electrically conductive surface of solid unfissured metal and plastic which is characterized by the absence of any pits, flaws, or irregularities greater than about three times the RMS microinch measurement of the surface.

The surface so obtained may be chromium plated for 5 hours in a bath containing 250 g./l. chromic acid, 2.5 g./l. sulfate ion derived from sulfuric acid, at temperature of 50 C. and cathode current density of 30 amperes per square decimeter to produce a hard chrome industrial finish.

The novel electrically conductive composition of this invention may comprise a resin vehicle, preferably a polyester typically formed by the reaction of 2 moles of glycerine and three moles of fumaric acid and then crosslinking with one mole of styrene, and a conductive powder containing 10%90%, say 50%, flaky iron particles and 90%l0%; say 50% fibrous iron particles. If desired the composition may be stored in the form of the uncrosslinked reaction product of e.g. glycerine and fumaric acid (to which no cross-linking agent such as styrene has been added) together with conductive powder.

It will be apparent to those skilled in the art that various changes and modifications may be made which come within the scope of this invention.

1 claim:

1. The process of electrodepositing a smooth level coating of metal on a basis metal containing surface depressions which comprises filling in the surface depressions with a viscous, electrically conductive resin containing 10%90% fiaky iron particles having a particle size of 177-74 microns and 90%l0% fibrous iron particles having a particle size of 2662 microns; hardening said resin; removing excess resin thereby forming a level surface; and electrodepositing a smooth level metal coating on said surface.

2. The process of electrodepositing a smooth level coating of metal on a basis metal containing surface depressions which comprises filling in the surface depressions with a viscous, electrically conductive polyester resin containing 10%-90% flaky iron particles having a particle size of 17774 microns and 90%l0% fibrous iron particles having a particle size of 2662 microns; hardening said resin; removing excess resin thereby forming a level surface; and electrodepositing a smooth level metal coating on said surface.

3. The process as claimed in claim 1 of electrodepositing a smooth level coating of metal on a basis metal containing surface depressions wherein said resin is prepared by the reaction of glycerine and fumaric acid, the reaction product being cross-linked by further reaction with styrene.

4. The process as claimed in claim 1 of electrodepositing a smooth level coating of metal on a basis metal containing surface depressions wherein said resin contains 50% by weight flaky iron and 50% by weight fibrous iron.

5. The process of electrodepositing a smooth level coating of chromium on a basis metal roll containing surface depressions which comprises filling in the surface depressions with a viscous, electrically conductive resin containing 10%90% flaky iron particles having a particle size of 177-149 microns and %l0% fibrous iron particles having a particle size of 2662 microns; hardening said resin; removing excess resin thereby forming a level surface; and electrodepositing a smooth level chromium coating on said surface.

6. A novel electrically conductive composition comprising a polyester resin vehicle, and a conductive powder containing 10%90% flaky iron particles having a particle size of 177-74 microns and -90%-10% fibrous iron particles having a particle size of 2662 microns.

7. A novel electrically conductive composition containing a polyester resin vehicle and a conductive powder containing 50% flaky iron particles having a particle size of 177-74 microns and 50% fibrous iron particles having a particle size of 2662 microns.

8. A novel electrically conductive composition containing a polyester resin vehicle formed by reacting two moles of glycerine and three moles of fumaric acid in the presence of a catalyst, and then cross-linking with one mole v of styrene; and a conductive powder containing 10%- 90% flaky iron particles having a particle size of 177-74 microns and 90%l0% fibrous iron particle having a particle size of 2662 microns.

References Cited UNITED STATES PATENTS OTHER REFERENCES Delmonte Metal Filled Plastics, Reinhold Co., 1961, pages 86, 107, 108 and 109 are relied on. TA 455 P 55 O 45.

JOHN H. MACK, Primary Examiner.

W. B. VAN SISE, Assistant Examiner. 

1. THE PROCESS OF ELECTRODEPOSITING A SMOOTH LEVEL COATING OF METAL ON A BASIS METAL CONTAIANING SURFACE DEPRESSIONS WHICH COMPRISES FILLING IN THE SURFACE DEPRESSIONS WITH A VISCOUS, ELECTRICALLY CONDUCTIVE RESIN CONTAINING 10%-90% FLAKY IRON PARTICLES HAVING A PARTICLE SIZE OF 177-74 MICRONS AND 90% FIBROUS IRON PARTICLES HAVING A PARTICLE SIZE OF 26-62 MICRONS; HARDENING SAID RESIN; REMOVING EXCESS RESIN THEREBY FORMING A LEVEL SURFACE; AND ELECTRODEPOSITING A SMOOTH LEVEL METAL COATING ON SAID SURFACE. 